Characterization of Candidate Materials for Remote Recession Measurements of Ablative Heat Shield Materials

Remote Recession Measurements of Wire-Seeded PICA Samples in an Arc-Jet Flow

“…The video indicates the aluminum spreading out at the surface with a maximum spot size around 18 s which corresponds to the maximum of Al emission with both spectrometers. From the average recession rate, the seeding depth should be reached by recession after 19 s. This phenomenon of Al emission showing up before recession reaches the seeding depth has been already observed in earlier tests, 4 and is similar to the TC emission for ICA-A explained by Al melting inside the PICA body and diffusing through the porous PICA most probably through capillary effects. As already hypothesized in the analysis of the PICA-A results, the same effects seem to occur with the thermocouple elements.…”

“…Surprisingly, that seems to be the case for aluminum as well in the tests with samples PICA-C and D, which is a different behavior from tests with Al embedded in PICA plugs where the Al emission usually showed clearly before the seeding depth was reached. 4 In the test with sample PICA-Z, aluminum shows up early and confirms the anticipated behavior. Also for silver, the results are ambiguous since very small differences between test video and emission spectra were found in the test with sample PICA-B while the PICA-Z results show a bad correlation between video and emission.…”

“…In the recent work, a methodology for recession measurements through the detection of seed elements buried at known depths inside the TPS material was developed. 3,4,5 The basic idea of remote recession sensing is to seed specific materials at a known depths inside the ablative material. Once recession reaches the seeding depth, the seed material comes in contact with the plasma, is gasified, and transported into the hot region of the post-shock layer by diffusion processes where the characteristic emission signatures can be detected by emission spectroscopy.…”

“…3 Seeding PICA samples though insertion of epoxy disks which contain the seed materials or through PICA plugs where the seed materials were introduced during the curing process has been demonstrated in arc-jet testing in the HYMETS facility at NASA Langley. 4,5 The most recent tests conclude the assessment of different seeding methods by investigating seeding of PICA through metal wires, mounted in the heat shield material like thermocouples. The advantage of this method is that the application of in-depth thermocouples is already flight qualified and accepted from a system engineering point of view.…”

Effect of Glass-Fabrics and High-Melting Powder Fillers on Thermal Protective Properties of Thermosetting Laminates

“…The use of modified plastics as ablative materials protecting against excessive temperature increase was connected with the middle of XX century, directly with arms industry as well as aeronautical, rocket and space techniques [1,2]. These materials can also be used in the design of passive fire-proof protections for large cubature supporting elements in building structures [3], communication tunnels [4,5] and for the protection of data stored in electronic, optical and magnetic carriers [6].…”